Which way do I turn a water pressure regulator screw?

Each manual says the same thing in its own words.

Watts, for its LF123 and LFN250 valves: "To readjust reduced pressures, loosen adjusting screw nut and turn adjusting screw clockwise to raise reduced pressure and counterclockwise to lower reduced pressure."

FEBCO, a Watts brand, for its PRV-2: "To adjust pressure setting, loosen the lock nut and turn the adjusting bolt clockwise to increase pressure, counter clockwise to decrease pressure."

Zurn Wilkins, for its Model 600XL, adds a picture of the motion: "turning adjustment bolt clockwise (into bell housing) to raise pressure or counterclockwise (out of bell housing) to reduce pressure." Turning in raises the setting, and backing out lowers it.

Three cautions appear in all of them. Loosen the locknut before you turn the screw. Use a gauge to verify the result. And don't bottom the screw out. Watts says "Do not bottom out adjusting screw or spring cage." Zurn says "Anytime a pressure reducing valve is adjusted, a pressure gauge must be used downstream to verify correct pressure setting. Do not bottom out adjustment bolt on bell housing."

A word on your own valve. The manuals above cover specific models, and we haven't read every valve on the market. If your valve has a nameplate, look up its model and read its sheet. If the screw doesn't move the number the way you expect, stop and read the manual or call a plumber.

Most PRVs come from the factory near 50 psi. FEBCO says "Regulator is factory preset to 50psi (345 kPa)," and Zurn says "All valves are factory set to approximately 50 PSI." Pressure from the street is reduced to that number, and your house sees it.

Where should the number land? EPA WaterSense says "WaterSense recommends incoming service pressure to be between 45 and 60 psi to ensure efficient use of water and proper system function." The plumbing code adds a ceiling: a valve "shall be installed to reduce the pressure in the building water distribution piping to not greater than 80 psi (552 kPa) static." So 45 to 60 is the sweet spot, and 80 is the hard limit.

Why raise it at all? A weak shower is a common reason. Zurn's troubleshooting guide covers it: "Pressure setting of reducing valve may be too low. Try increasing the setting of the reducing valve gradually to increase flow at the fixtures." Our page on increasing water pressure safely covers the other causes to rule out first. Why lower it? Banging pipes, dripping faucets or a leaking relief valve on a high reading. See why pressure suddenly gets too high.

You need a pressure gauge that screws onto a hose bib and a wrench that fits the locknut. Adjust only your own valve. In Phoenix the private regulator on your side of the meter is the homeowner's. The city's customer page says "Private pressure regulators are the responsibility of the homeowner."

1. 1Attach the gauge. EPA's verification steps: "Attach a pressure gauge to a hose bibb, the cold-water faucet for the washing machine hookup, or a cold-water faucet on the first floor. Turn on the water to the fully open position." Use the hose bib closest to the valve if you can.
2. 2Get a starting number. With all water off in the house, read the gauge. That's your static pressure.
3. 3Loosen the locknut on the adjustment screw.
4. 4Turn the screw a little. Clockwise to raise, counterclockwise to lower. Go in small turns. Zurn's own advice on raising pressure is to do it "gradually."
5. 5Relieve pressure if you're lowering it. Zurn's note: "When reducing pressure open a downstream faucet to relieve pressure and use a pressure gauge (Wilkins Model HGI-25) to verify correct downstream pressure setting." The pressure already in your pipes doesn't drop on its own when you back the screw out, so the reading can look stuck. Run a faucet briefly, then read again.
6. 6Read the gauge with everything off. Repeat steps 4 through 6 until it sits where you want.
7. 7Tighten the locknut. Zurn says "Tighten locknut when desired pressure is achieved and test valve to confirm proper operation."
8. 8Test it. Run water, shut it off, and watch the gauge. Zurn's check is to "Observe the gauge for 10 minutes." If the pressure holds, the valve is sealing. If it "slowly creeps up within 10 minutes the valve may be fouled and should be cleaned and retested."

That last result isn't an adjustment problem. Creeping pressure, a screw that does nothing, or a reading that swings are signs of a failing valve. See the signs a pressure reducing valve is going bad.

Raising the setting is not free. A PRV makes your plumbing a closed system, so when the water heater runs, the extra volume has nowhere to go. Watts says "When reducing valve is used, it makes a closed system; therefore, pressure relief protection must be provided on the downstream side of the reducing valve to protect equipment." A higher starting point gives you less room before the heater's relief valve opens.

The plumbing code requires a thermal expansion control device on the heater's cold supply where the water passes through a check valve, pressure reducing valve or backflow preventer, and it must be sized so the system pressure doesn't exceed the 80 psi limit. If your relief valve starts to drip after you raise the setting, that is the first place to look. Our page on whether you need an expansion tank explains how it works, and why a water heater relief valve leaks shows what a drip means.

Also mind where the valve sits and who can reach it. The PRV goes on the owner's side of the meter, and our page on where a pressure reducing valve goes shows the layout.

One more reason to take a reading now and then: Zurn's notice says "Periodic inspection and maintenance is required of all plumbing system components, at least once per year or more as service conditions warrant." A yearly gauge check takes five minutes and tells you whether the valve is still holding the setting you chose. Write the number on the valve or in your phone so you know what normal looks like.

Turning a screw is simple. Judging what the reading means is the harder part. Call a licensed plumber if the gauge shows more than 80 psi and the screw doesn't bring it down, if the pressure is unstable, if the valve leaks at the screw, or if you can't find the model. HQ Plumbing & Air can test your pressure, set or replace a PRV, and check the expansion tank while we're there. Estimates are free, the price comes up front before work starts, and we're licensed, insured and available 24/7.

Here's the play. Clockwise up, counterclockwise down, small turns, a gauge on every change, and the locknut tightened when you're done.